United Star PRC-148 programming cable

По просьбам зарубежных трудящихся.

Schematics

United Star uses a common bus, much like 1-wire, but using RS-232 protocols. Only two wirec must be connected to radio - ground and output (common bus).

Schematics are simple. Two N-ch transistors, first acts as an inverter, second acts as a pull-down. When we transmit, it pulls down common bus to ground.

When receiving, we listen for a bus and this time radio pulls down common bus as it transmits.

Because it is a low voltage bus, we have to use COM TTL adapters. Personally, I prefer  cp2102 ones from aliexpress (see below for connection).

Parts and layout

As a lazy ass I hate drilling, so I use an smd components. Both transistors are most common type - 2n7002. Resistors are 0603 size (but you can use 0805 or 1206 it you like).

Just mount it on a piece of a breadbord.

Connection

All you need is a usb-comttl and a 2.5mm jack. Connect output to central contact, and ground to sleeve.

Software

Just download comttl drivers (cp2102 drivers page).

After connecting cable to usb you have to check it registers itself as a COM1/2/3/4, United Star software cannot use any COM port above that.

Here's instruction how to change COM port in windows.

Connect cable to radio, switch power and use United Star software provided with the radio.

I was able to program it with that cable even under MacOS, using virtual machine (VmWare Fusion) with Windows 7 installed.